Example from a Bio 2 class on the tongue rolling trait.



Known information: Tongue rolling is through to be inherited by a dominant allele (R)
A survey of a class 22 people was taken and the following results were found:
  • 4 people can't roll their tongue (rr - genotype)
  • 18 people can roll their tongue (RR + Rr - genotypes)


Calculating the Allele Frequencies

Let p stand for the dominant allele (R) and q stand for (r).
Since the total number of alleles in the population is made up of p+q

p+q=1

Each individual has two alleles, frequency of RR + Rr + rr = 1. Therefore we can express this equation as: p² + 2pq + q² = 1

  1. We know that 8 alleles out of 44 are rr, so q² = 8/44 = 0.18 so q = square root of 0.18 = 0.42
  2. Now we can solve for p. p = 1 - q = 1 - 0.42 = 0.58
  3. We can now calculate how many people in the class are likely:
  • RR = p² = 0.34
  • Rr = 2pq = 0.48
  • rr = q² = 0.18